If you’ve tried all of the basic ways to manage your email, but are still feeling overwhelmed, try setting quotas. The idea is that the more messages you send, the more you get. Assume that every email you send will generate 4–10 responses, so you’re creating work for yourself with each message. Limit the number of threads you initiate each day. For incoming messages, estimate the number of emails each will generate and make that your daily quota. Use filters to sort incoming mail and keep all but the most crucial messages out of your inbox. Auto-file other messages in alternative folders. Keep adding rules until your daily inbox volume falls below the quota you’ve set.
Adapted from the HBR Guide to Getting the Right Work Done.